The present invention relates to a pneumatically operated screw driver preferably used for screwing a threaded fastening member to a woody material or the like.
Various pneumatically operated screw drivers have been conventionally proposed. According to a typical arrangement of the pneumatically operated screw drivers, a driver bit is rotated by an air motor to screw a threaded fastening member. For example, the Japanese Patent Application Kokai No. Hei 64-45579 discloses a screw driver having a driver bit moving downward together with an air motor. The Japanese Patent Application Kokai No. Hei 5-261676, corresponding to the U.S. Pat. No. 5,231,902 (DEP 4219032), discloses another type of screw driver having a driver bit moving downward independent of a stationary air motor.